Study of turbulence modulation and core density peaking with CO 2 laser collective scattering diagnostics in EAST tokamak

Progress from experiment in understanding the interaction between electron-scale turbulence and plasma poloidal flow in tokamak is reported. Multiple electron-scale turbulence (for 0.8 ≤ kθρs ≤ 4) in plasma radial region (ρ = 0-0.8) is simultaneously monitored by CO2 laser collective scattering diagnostics in EAST tokamak. In stable discharge phase with ECRH power modulation and constant NBI injection, a periodically change of core density peaking factor (〈ne(0)〉/〈ne(0.5)〉) can be obtained. We note that the intensity of turbulence and core density peaking factor show a negative correlation, while the poloidal rotation speed is inversely proportional to the intensity of electron-scale turbulence. The correlation between turbulence and plasma flow are found closely related to the density peaking factor. The quasi-linear theory of electron-scale turbulence driven intrinsic poloidal rotation is adopted, and it shows that plasma flow may exhaust the free energy of turbulence through Reynolds stress. Besides, by comparing the plasma flow shear and spatial cross-correlation of turbulence, we observed that the spatial structure of turbulence at kθ = 12 cm-1 is more sensitive to flow shear than that of turbulence at kθ = 22 cm-1. The possible mechanism for controlling the core density peaking (ρ = 0-0.5), together with unchanged density gradient in outer (ρ = 0.5-0.8), are favorable for controlling fusion reactions rate if they can be extrapolated to burning plasma. The results in ECRH power modulation experiments without NBI are listed and analyzed simultaneously, which serve as a comparison and enrich the physical picture.